Conventionally, there has been known a heat exchanger including a pair of upper and lower headers horizontally facing each other, a plurality of flat heat transfer tubes communicatively connected to these headers such that the plurality of flat heat transfer tubes are in parallel with each other at a regular interval, and a corrugated fin interposed into a gap between the flat heat transfer tubes in close contact therewith. In the heat exchanger, refrigerant serving as a heat exchange medium flows in the plurality of flat heat transfer tubes simultaneously in parallel.
When heating operation is performed in a cold climate using such a heat exchanger as a heat pump-type outdoor unit for air conditioning for both cooling and heating, frost forms on surfaces of the fin and the heat transfer tubes, and heat exchange efficiency is decreased.
As a measure against such frost formation, Japanese Patent Laying-Open No. 9-280754 (PTD 1) discloses a heat exchanger including a corrugated fin disposed to protrude on windward side from flat heat transfer tubes, and louvers formed only in a leeward portion.